This invention relates in general to hydraulic controls and more particularly to directional control valves for controlling pressure fluid actuating a hydraulic cylinder.
Manually operated hydraulic directional control valves are well known for controlling power cylinders in a wide variety of applications. Manual operation is provided by a lever mounted at one end of the valve housing and connected by a linkage to the longitudinally movable valve spool. Semi-automatic operation is provided by a valve positioning unit mounted on the other end of the valve housing. Such units include a pair of biasing springs which bias the valve spool to its neutral or center position, and a detent mechanism for holding the valve spool in either power position until pressure buildup indicates the power stroke of the cylinder has been completed.
Pilot controlled directional control valves are also well known in the art. These valves have included two cylinders mounted at opposite ends of the valve spool, one cylinder pushing the spool in one direction and the other cylinder pushing the spool in the opposite direction. Manual operation of these valves is not possible.
Where both remote control and manual operation at the valves are desired, it has been customary to operate the valves from the remote point by push pull cables. The cables often present an an installation problem especially in mobile applications with tilt cab vehicles. In addition, after a period of time these cables become unreliable.